<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var money = 100;

        while (num != 4) {
            var num = prompt('请输入您要的操作：' + '\n' + '1.存钱' + '\n' + '2.取钱' + '\n' + '3.显示余额' + '\n' + '4.退出' + '\n');
            if (num == 1) {
                var m1 = prompt('请输入你要存入的金额：');
                var money = parseFloat(m1) + money;
                alert('你的余额是' + money + '元');
         
                continue;

            } else if (num == 2) {
                var m2 = prompt('请输入你要取出的金额：');
                var money = money - parseFloat(m2);
                alert('你的余额是' + money + '元');
                continue;
            } else if (num == 3) {
                alert('你的余额是:' + money);
                continue;
            } else {}
        }
    </script>
</head>

<body>

</body>

</html>